Both long-chain and short-chain fatty acids are transported by group translocation mechanisms in Escherichia coli. A long-chain acyl CoA synthetase catalyzes the translocation of long-chain fatty acids and acetyl CoA: short-chain fatty acid CoA transferase catalyzes the translocation of short-chain fatty acids. Both enzymes are membrane- bound. Some aspects of the CoA transferase catalytic mechanism have been determined. Proposed work deals with structure-activity relationships of the solubilized, purified CoA transferase; these studies are being correlated with the transporting function of the enzyme as studied in isolated membrane vesicles. Two approaches are being used to investigate how the rate of acetoacetate transport might be regulated. First, the Beta-ketothiolase is being purified. This enzyme catalyzed the CoA-dependent cleavage of acetoacetyl CoA to two equivalents of acetyl CoA. By determining the affinity of the thiolase for acetoacetyl CoA, the product of the translocation step, and the equilibrium constant for the thiolase reaction, we can determine how the CoA transferase and thiolase, in concert, affect the flux of acetoacetate into the cell. Second, the effect of the RNA synthesis control gene (rel) on short chain fatty acid transport is being investigated. This gene has been shown to be involved in the regulation of not only RNA synthesis during amino acid starvation, but also a host of other cellular functions, including the transport of glucosides, purines and pyrimidines as well. Finally, studies are being conducted to distinguish the localization(s) of fatty acid Beta-oxidation enzymes of E. coli which have specificities for long- and short-chain acyl CoA substrates. These studies are being conducted preliminary to determining how the rate of Beta-oxidation is controlled in E. coli, since it has been demonstrated that long-chain fatty acid uptake is tightly coupled to subsequent oxidation.